The spirit of the web server is " do not touch the Mybook Original Configuration lines in lighttpd.conf " , instead, add new lines and create lines for other Web sites listening on different ports If you modify these lines, you take the risk to scratch your standard Web admin interface.

A mime type line may also be usefull if you want to launch Windows media player when clicking a link.
(i think there is a post somewhere in the Forums explaining the exact mime line that must be added…